The present invention relates to skateboards, and more specifically to the wheels used for skateboards.
Conventional skateboards have an elongated plank or platform sized for supporting a person in a standing position and a pair of set of fore and aft wheels secured beneath the board. Such a skateboard is described in U.S. Pat. No. 3,565,454 issued to Richard Lawrence Stevenson.
Wheels for skateboards can define a cylindrical tread section having sharp or broken edges such as the wheel shown in the above-mentioned U.S. Pat. No. 3,565,454. A problem with such wheels is that when the board tilts when it is used for acrobatic maneuvers and turns, there is a tendency for a portion of the wheels to tilt away from the ground with resultant sliding of the skateboard. Another problem is that because of the sharp edge of the cylindrical thread portion, reduced tread surface is available when the skateboard tilts when cornering or turning, thus making the board difficult to control. In addition, instability when going over bumps, twigs and the like is incurred with such wheels.
Attempts have been made to overcome the disadvantages of wheels having sharp edged cylindrical tread sections by providing deformable lips or extensions on one or both edges of the tread section. Wheels with such lips have increased traction and resistance to sideways slip but result in considerable loss of speed during sharp turns due to greatly increased rolling friction as a result of lip deformation. Also such a lip can deform and fold under the main portion of the wheel when the lip contacts the edge of a raised portion of the surface being traveled over such as a crack or other irregularity in the riding surface, especially when the direction of travel is not perpendicular to such obstacles or surface irregularities. Both of these conditions can result in sudden loss of speed and can lead to a rider being thrown from the skateboard with resultant injuries.
Thus there is a need for skateboards having wheels which provide sufficient tread area for adequate traction when cornering or turning, and which easily travel over bumps, rocks, twigs, raised areas, and the like, without sudden loss of speed.